The deposition of organic contaminants on process equipment, screens, and containment vessels in papermaking can reduce process efficiency and paper quality. Deposits on machine wires, felts, foils, headbox surfaces, screens, and instruments can result in downtime for cleaning to avoid the problems associated with poor process control, reduced throughput, and substandard sheet properties. Such contaminants are generically referred to in the paper industry as either “pitch” or “stickies.” As used herein, “pitch” generally refers to tacky materials containing resins derived from wood fibers. As used herein, “stickies” generally refers to tacky materials derived from recycled paper products (e.g., printing inks or pressure sensitive adhesives). Such substances can form deposits when reintroduced in recycled fiber systems. Pitch and stickies may also contain entrapped inorganic materials such as talc, calcium carbonate, or titanium dioxide.
Recycled fiber refers to secondary fibers that are repulped to provide the papermaking furnish with raw material for the production of new paper. The secondary fibers may be either pre-consumer or post-consumer paper material that is suitable for use in the production of paper products. Sources of secondary fiber may include old newspaper (“ONP”), old corrugated cardboard (“OCC”), mixed office waste (“MOW”), computer printout (“CPO”), ledger, etc. These once-processed papers contain various types of adhesives (e.g., pressure sensitive, hot melts, etc.), inks, and coating binders.
Pitch and stickies are each hydrophobic in nature and thus unstable as colloids in aqueous papermaking environments, thereby facilitating their deposition onto surfaces of the paper machine. Problems that may arise from deposition are as follows: (1) reduced throughput due to plugging of forming fabrics and press felts, (2) sheet holes or paper breaks due to large deposits breaking loose from the equipment, and (3) reduced sheet quality due to large particle contaminants incorporated in the final sheet.
Surfactant additives can be used to disperse pitch and stickies, but current products have limitations. For example, cationic polymer dispersants can be attracted to fiber surfaces, which may reduce their effectiveness, and they may further interfere with charge dynamics of the fibers, which may decrease the effectiveness of other additives such as strength agents. Anionic polymer dispersants may cause precipitation of wet strength agents or inorganic components. Nonionic surfactants such as nonylphenol ethoxylates may cause foaming, which can upset the system. Accordingly, improved methodologies for controlling contaminant deposition in the papermaking process are needed.